The development of optical fiber telecommunications has put in evidence the interest of wavelength multiplexing of numerous signals that are also frequency-shifted.
It is in this framework that so-called interleaver devices have been used and wherein two combs of multiplexed wavelengths such as represented respectively on FIGS. 1 and 2, are addressed on the inputs E1 and E2 of a two-wave interferometer.
The response of the interferometer for each of the inputs E1 and E2 being respectively R1 and R2, suitable adjustment of the interferometer enables multiplexing of both combs of wavelength respectively P1 (xcex1, xcex3, . . . , xcex2p+1) and P2 (xcex2, xcex4, . . . , xcex2p) without any significant energy losses.
The interest of such devices which have been described above is therefore easily understood.
More precisely, in a conventional fashion, such a two-wave, optical fiber interferometer has been realised while using two couplers, the first input coupler is C1, separating both waves which, after following optical paths, are recombined by the coupler C2, for instance, an interferometer of Mach-Zehnder such as represented on FIG. 4.
Adjusting the (step difference) travel length between both optical paths enables to interleave both combs of wavelengths respectively P1 (xcex1, xcex3, . . . , xcex2p+1) and P2 (xcex2, xcex4, . . . , xcex2p) such as represented on FIG. 3 in order to provide a multiplexed flux of interleaved wavelengths (xcex1, xcex2, xcex3, . . . , xcex2p, xcex2p+1).
Thus, the operation of this device as a multiplexer has been described, interleaving combs of wavelengths. Obviously, such a device is reversible and may, in reverse direction, as a demultiplexer, separate combs of interleaved wavelengths.
However, restitution of very high quality signals calls for increased control of the multiplexing/demultiplexing stages.
The purpose of this invention is therefore to suggest an optical device for interleaving or dissociating a set of wavelength-multiplexed signals, simple in its design and in its operating mode, and which does not cause any losses.
To that end, the invention concerns an optical device for wavelength dissociation receiving a multiplexed flux of interleaved wavelengths (xcex1, xcex2, xcex3, . . . , xcex2p, xcex2p+1) and generating a first and a second dissociated multiplexed fluxes, respectively (xcex1, xcex3, . . . , xcex2p+1) and (xcex2, xcex4, . . . , xcex2p), the frequency interval between two interleaved wavelengths xcex2p, xcex2p+1 being xcexf1.
According to the invention, this optical device comprises schematically:
a fiber forming an input gate of the optical device,
a circulator linked to said fiber and comprising a first and a second output fibers of said circulator,
the second output fiber forming a first output gate of the optical device for the first dissociated multiplexed flux (xcex1, xcex3, . . . , xcex2p+1),
the first output fiber of said circulator being linked to an optical assembly by a collimation lens, said optical assembly defining a closed optical path consisting of:
a polarisation beam splitter having polarisation axes receiving the flux going through the collimation lens and separating it into two contrapropagating components (r1) and (r2) on the optical path,
means for transferring the luminous flux along the closed optical path,
a birefringent medium having birefringent axes interposed on the optical path, said birefringent medium modifying the polarisation state of the flux going through it as a function of the wavelength, fluxes with wavelengths (xcex2, xcex4, . . . , xcex2p) of the components (r1) and (r2) not being modified, the polarisation of the fluxes with wavelengths (xcex1, xcex3, . . . , xcex2p+1) being interchanged between said components so that the polarisation beam splitter orients distinctly said first and second output-multiplexed fluxes,
and in that the optical device comprises a fiber forming a second output gate of the optical device, and whereof the end is located at the focus of a collimation lens which receives said second dissociated multiplexed flux (xcex2, xcex4, . . . , xcex2p) of the polarisation beam splitter.
The invention also concerns an optical device for wavelength interleaving receiving a first and a second multiplexed fluxes, respectively (xcex1, xcex3, . . . , xcex2p+1) and (xcex2, xcex4, . . . , xcex2p), and generating a multiplexed flux of interleaved wavelengths (xcex1, xcex2, xcex3, . . . , xcex2p, xcex2p+1), the frequency spacing interval between two interleaved wavelengths xcex2p, xcex2p+1 being xcexf1.
According to the invention, this optical device comprises schematically:
a fiber forming an output gate of the optical device for the multiplexed flux of interleaved wavelengths (xcex1, xcex2, xcex3, . . . , xcex2p, xcex2p+1).
a circulator linked to said fiber and comprising a first and a second output fibers of said circulator,
the second output fiber forming a first input gate of the optical device for a first multiplexed flux (xcex1, xcex3, . . . , xcex2p+1),
the first output fiber of said circulator being linked to an optical assembly by a collimation lens, said optical assembly defining a closed optical path consisting of:
a polarisation beam splitter having polarisation axes receiving the flux going through the collimation lens and separating it into two contrapropagating components (r1) and (r2) on the optical path,
means for transferring the luminous flux along the closed optical path,
a birefringent medium having birefringent axes interposed on the optical path, said birefringent medium modifying the polarisation state of the flux going through it as a function of the wavelength, the polarisation of both multiplexed fluxes (xcex1, xcex3, . . . , xcex2p+1) and (xcex2, xcex4, . . . , xcex2p) being interchanged between said components so that the polarisation beam splitter orients said multiplexed fluxes towards the output gate of the device,
and in that the optical device comprises a fiber forming a second input gate of the optical device for the second multiplexed flux (xcex2, xcex4, . . . , xcex2p), and whereof the end is located at the focus of a collimation lens which sends said second flux on the polarisation beam splitter.
In different particular embodiments having each its particular advantages and lending themselves to numerous technically possible combinations:
said birefringent axes of the birefringent medium are oriented at 45xc2x0 with respect the axes of the polarisation beam splitter,
the birefringent medium is a birefringent crystal,
the birefringent medium is a birefringent optical fiber,
the polarisation beam splitter is a polarisation beam separator cube,
transferring means are flat mirrors, placed at 90xc2x0, the assembly comprising the mirrors and the separator forming a closed loop.
Advantageously, the assembly of these components can be realised using fibers or still integrated optical components.
The invention also concerns an optical switch.
According to the invention, this switch contains a device for wavelength interleaving or dissociation such as defined above and according to the invention, it also contains a liquid crystal and control means receiving an electrical signal.